If it is a factory KDX silencer, it has a spark arrestor inside the unit. Also, look close on the unit and it should be stamped into the outside indicating that it is a forrestry approved unit (which means it has a spark arrestor inside). If it is an FMF "Turbine Core" silencer, it has a spark arrestor in it.
JCW is right if its a spark arrestor it will be stamping somewhere on the silencer indicating its a spark arrestor and has been approved by the U.S. Forest Service.
does the FMF Power Core II silencer have a spark arrestor? if a forest ranger or someone like them caught you in the forest without one could u be fined?